JP2019181863A - Method for creating numerical expression for prediction of printing result, prediction method, and prediction system - Google Patents

Abstract

To suitably perform prediction of a printing result when using, for example, a characteristic ink.SOLUTION: A method for creating a numerical expression for prediction of a printing result in which the numerical expression for prediction of a printing result is a numerical expression used for prediction of a result of printing performed by use of an ink. This method comprises: a pattern printed matter creation stage (S102) which is a stage of creating a printed matter for evaluation which is used for evaluation of printing result, and at which the printed matter for evaluation, which includes a pattern od which a printing density is differed at plural stages, is created; a measuring stage (S104) at which a bidirectional reflectance distribution function is measured in association with the printing density; and a numerical expression creation stage (S106) which is a stage of calculating a numerical expression of prediction of a printing result on the basis of a measurement result at the measuring stage, and at which the numerical expression of prediction of a printing result is created on the basis of at least the bidirectional reflectance distribution function associated with the printing density.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a printing result prediction formula creation method, a prediction method, and a prediction system.

  Conventionally, in the field of printing apparatuses such as inkjet printers, color printing is performed using primary colors (basic colors) such as C (cyan), M (magenta), Y (yellow), and K (black). Widely done. Further, in recent years, a method using a special color other than these primary colors has been established for the purpose of expressing a color (white or the like) or a texture (metal gloss or the like) that cannot be reproduced only by these primary colors. As prior art documents in the field to which the present invention relates, the following Patent Document 1 and Non-Patent Documents 1 to 4 are conventionally known.

JP 2010-114506 A

Huntsman, James R. "A new model of dot gain and its application to a multilayer color proof." Journal of Printing Science and Technology 24.3 (1987): 189-202. Kehren, Katharina, Philipp Urban, and Edgar Dorsam. "Bidirectional Reflectance and Texture Database of Printed Special Effect Colors." Color and Imaging Conference. Vol. 2011. No. 1. Society for Imaging Science and Technology, 2011. Ngan, Addy, Fredo Durand, and Wojciech Matusik. "Experimental analysis of brdf models." Rendering Techniques 2005.16th (2005): 2. Hebert, Mathieu, and Roger D. Hersch. "Yule-Nielsen based recto-verso color halftone transmittance prediction model." Applied optics 50.4 (2011): 519-525.

  In the field of printing, in order to perform high-quality printing, it may be necessary to predict a printing result (print finish) using a color proofing system or the like. Further, when spot color ink is used, as described above, colors, textures, and the like that cannot be reproduced using only primary color inks can be appropriately realized. In such a case, it is considered that printing result prediction is important.

  On the other hand, such special color inks are not based on normal primary color inks (for example, CMYK inks) and have different optical characteristics, so that they can be expressed in a color calibration system such as a conventional color management system (simulation). ) May be difficult. More specifically, in the field of printing apparatuses such as inkjet printers, ink that expresses colors by a subtractive color mixing method, such as CMYK inks, is usually used. Therefore, in a conventional color proofing system, conversion from a color expressed by an additive color mixing method such as an RGB color system color into a color expressed by a subtractive color mixing method such as a color of a CMYK color system is usually performed. Do. On the other hand, if the optical characteristics of the primary color ink and the special color ink are different, it is difficult to appropriately express the texture and the like realized during printing with the special color ink. That is, conventionally, it may be difficult to appropriately express the texture of a printing result performed using spot color ink in a color calibration system. In this case, the fact that the printing result cannot be predicted in advance has also been a cause of hindering the spread of spot color inks.

  With respect to this point, Patent Document 1 uses a parameter of a bidirectional reflectance distribution function (BRDF) for the purpose of displaying a texture that matches the texture of the printed surface of the printed material on a display or the like. Etc. are described. As a specific method, a look-up table that represents the correspondence between the print data value and the texture information data value is created based on the measurement result of the bidirectional reflectance distribution function. It is described that to get.

  However, when the method disclosed in Patent Document 1 is used as it is, for example, although it is possible to predict the texture and the like of the print result objectively and in detail, enormous man-hours are required for the work of creating the lookup table. It may take. More specifically, when the method of Cited Document 1 is actually performed, it is considered necessary to perform detailed measurement of the bidirectional reflectance distribution function while changing a plurality of parameters in detail. In this case, the work of creating the lookup table may take several days to 10 days or more.

  Therefore, conventionally, it has been desired to more appropriately predict the printing result performed using the special color ink. Therefore, an object of the present invention is to provide a printing result prediction formula creation method, prediction method, and prediction system that can solve the above-described problems.

  The inventor of the present application has conducted extensive research on a method for predicting a printing result using a special color ink in a color proofing system or the like. Moreover, in this earnest study, as a prediction method, a model formula was created based on the measurement result of the bidirectional reflectance distribution function (BRDF), and the prediction was performed according to the model formula. Further, through further earnest research, the number of man-hours required for measuring the bidirectional reflectance distribution function is greatly reduced by using a model formula with sufficient accuracy for the human eye ability. It has been found that the prediction can be performed more easily than the disclosed method. Further, through further earnest research, the inventors have found characteristics necessary for obtaining such an effect and have reached the present invention.

  In order to solve the above problems, the present invention provides a printing result prediction formula creation method for creating a printing result prediction formula, which is a formula used for prediction of a printing result performed using an ink, wherein the ink is A printed matter for evaluation which is a printed matter used for evaluation of a printing result to be used, and the printed matter for evaluation including a pattern in which a printing density which is an amount of ink per unit area is varied in a plurality of steps is created. A pattern printed matter creation step, a step of measuring a bidirectional reflectance distribution function for the evaluation printed matter, a measurement step of measuring the bidirectional reflectance distribution function in association with the print density, and the measurement step Calculating the print result prediction formula based on the measurement result of the print result prediction, based on at least a bidirectional reflectance distribution function associated with the print density Characterized in that it comprises a formula creation step of creating a formula.

  When configured in this manner, by creating a printing result prediction formula that is a model formula, it is possible to appropriately predict the printing result in, for example, a color calibration system. Also, in this case, for example, by creating a printing result prediction formula with sufficient accuracy for the human eye ability, it is possible to create a formula appropriately without enormous man-hours. Therefore, if constituted in this way, prediction of a printing result can be performed appropriately, for example.

  More specifically, the printing result prediction formula created by the above configuration may be used in, for example, a printing result prediction method or prediction system. In this case, for example, it is conceivable that the printing result is predicted using the created printing result prediction formula, and an image indicating the predicted printing result is displayed on the display device.

  Further, the inventor of the present application has found that the print result can be predicted more appropriately by further performing an operation in the subjective evaluation stage in the above-described configuration through further earnest research. In this case, the subjective evaluation stage is, for example, a stage in which subjective evaluation is performed on the evaluation printed material created in the pattern printed material creating stage. In this case, at the subjective evaluation stage, for example, at least a part of the print density in a plurality of stages is selected by subjective evaluation. In the subjective evaluation stage, it is conceivable to perform subjective evaluation by a known method such as the SD method (Semantic Differential Method). In this case, in the formula creation stage, for example, a formula for predicting the result is created based at least on the bidirectional reflectance distribution function associated with a part of the print density selected in the subjective evaluation stage.

  If comprised in this way, the evaluation which reflected the capability of human eyes can be performed appropriately by subjective evaluation, for example. This also makes it possible to more appropriately create a printing result prediction formula with sufficient accuracy for the human eye ability. Further, in this case, by using subjective evaluation, for example, even when only a bidirectional reflectance distribution function corresponding to a small number of types of printing density is measured, a printing result prediction formula can be created more appropriately. . Therefore, if constituted in this way, prediction of a printing result can be performed more simply and appropriately, for example.

  Here, in this configuration, as printing performed using ink, for example, it is conceivable to perform printing by an inkjet method. The print result prediction formula is used in, for example, a calculation performed to display the predicted print result on a display device in a color proofing system or the like. If comprised in this way, the numerical formula for printing result prediction can be used appropriately in the color calibration system for inkjet printers, for example.

  In this configuration, for example, glossy special color ink is used as the ink. The spot color inks are inks other than primary color inks such as CMYK color inks based on subtractive color mixing. Further, using the glossy special color ink may be, for example, using a glossy special color ink in addition to the primary color ink. Further, for example, in the case of further using a primary color subset ink based on subtractive color mixing in addition to the primary color ink, the special color ink is considered to be, for example, an ink other than the primary color ink based on the subtractive color mixture and the subset ink. You can also. Further, as the glossy special color ink, for example, it is conceivable to use a silver color ink or the like. When such special color ink is used, at the subjective evaluation stage, for example, it is conceivable to evaluate whether or not the glossiness is felt in association with at least the print density. If comprised in this way, when using the ink of a glossy special color, subjective evaluation can be performed appropriately, for example. In addition, for example, it is possible to more appropriately create a printing result prediction formula using subjective evaluation. In the subjective evaluation stage, for example, the degree of gloss may be further evaluated in association with the print density. If comprised in this way, when using the ink of a glossy special color, a more detailed subjective evaluation can be performed appropriately.

  In this configuration, for example, the operation at the measurement stage may be performed before the operation at the subjective evaluation stage or in parallel with the operation at the subjective evaluation stage. In this case, at the measurement stage, for example, it is conceivable to measure a bidirectional reflectance distribution function corresponding to all of the print densities in a plurality of stages. If comprised in this way, the measurement of a bidirectional | two-way reflectance distribution function can be started at an early stage, without waiting for the result of subjective evaluation, for example. Also, in this case, by measuring a bidirectional reflectance distribution function corresponding to a larger print density regardless of the result of the subjective evaluation, for example, when performing various analyzes or the like, parameters that can be used are set. More can be secured.

  Further, the operation at the measurement stage may be performed after the operation at the subjective evaluation stage, for example. In this case, only the bidirectional reflectance distribution function corresponding to a part of the print density may be measured using the result of the subjective evaluation. More specifically, in this case, at the measurement stage, for example, a bidirectional reflectance distribution function corresponding to only a part of the print density including the print density selected at the subjective evaluation stage among the multiple stages of print density is obtained. It is possible to measure. If comprised in this way, the man-hour required for the measurement of a bidirectional | two-way reflectance distribution function can be reduced more, for example. This also makes it possible to more efficiently create, for example, a print result prediction formula.

  Further, in this configuration, in the formula creation stage, for example, by performing approximation using the least square method on the bidirectional reflectance distribution function associated with a plurality of print densities, the print result prediction formula is obtained. It is possible to create. When performing subjective evaluation, for example, an approximation using the least square method may be performed on the bidirectional reflectance distribution function associated with a part of print density selected in the subjective evaluation stage. Conceivable. In this case, it is conceivable to create one print result prediction formula for the print density range including all the print densities selected in the subjective evaluation stage. If comprised in this way, the numerical formula for printing result prediction can be produced appropriately based on the measurement result of a bidirectional | two-way reflectance distribution function, for example.

  According to the present invention, for example, it is possible to appropriately predict a printing result.

FIG. 5 is a diagram for describing a model formula according to an embodiment of the present invention, and illustrates an example of a configuration of a printing system 10 that uses the model formula. An example of the measurement result of BRDF measured at the time of creation of a model formula, and an example of the output of a model formula are shown. FIG. 2A shows an example of a BRDF measurement result. FIG. 2B shows an example of the output of the model formula. It is a figure explaining in more detail how to create a model formula. FIG. 3A shows an example of a patch to be printed in this example. FIG. 3B is a flowchart illustrating an example of an operation for creating a model formula. It is a flowchart which shows the modification of the operation | movement which produces a model formula. It is a figure explaining the usage of the patch in this modification. FIG. 5A shows an example of a patch to be printed in this modification. FIG. 5B shows an example of a patch selected by subjective evaluation. FIG. 5C shows a modification of the patch selected in the subjective evaluation. It is a figure explaining the further modification of the operation | movement which produces a model formula.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. 1 and 2 are diagrams for explaining a model formula according to an embodiment of the present invention. FIG. 1 shows an example of the configuration of a printing system 10 that uses a model formula. FIG. 2 shows an example of a measurement result of BRDF (bidirectional reflectance distribution function) measured at the time of creating a model formula, and an example of an output of the model formula. FIG. 2A shows an example of a BRDF measurement result. FIG. 2B shows an example of the output of the model formula.

  In this example, the printing system 10 is a printing system capable of performing color calibration, and performs color calibration by predicting a printing result using a model formula which is an example of a printing result prediction formula. In this case, the printing result prediction formula is, for example, a formula used for prediction of a printing result performed using ink. Further, the color calibration operation performed in the printing system 10 of this example can be considered as an example of an operation of a prediction method for predicting a printing result when printing is performed using ink. Further, the printing system 10 can be considered as an example of a prediction system that predicts a printing result, for example.

  In this example, BRDF is measured when creating the model formula. The method of creating the model formula will be described in more detail later. Except as described below, the printing system 10 of this example may have the same or similar features as the known printing system 10.

  In this example, the printing system 10 includes a printing device 12, a color calibration PC 14, and a display device 16. The printing apparatus 12 is an ink jet printer that performs printing by an ink jet method, receives print data that has undergone color calibration from the color calibration PC 14, and prints an image indicated by the print data. As the printing apparatus 12, for example, a known ink jet printer can be suitably used. Further, the printing apparatus 12 uses process color inks and special color inks as inks used for printing. In this case, the process color inks are, for example, primary color (basic colors) inks for performing color expression by mixed colors during printing. More specifically, in this example, the printing apparatus 12 uses C (cyan), M (magenta), Y (yellow), and K (black) inks as the process color inks. Is used. The special color ink is an ink other than primary color inks such as CMYK color inks. The spot color ink can be considered as, for example, an ink used for expressing a color or texture that is difficult to express only with the primary color ink. In this example, at least silver ink is used as the special color ink. In this case, the silver ink is an example of a glossy special color ink. As the silver ink, for example, an ink that can express metallic luster by including a metal pigment such as aluminum (for example, scaly pigment) can be suitably used. Further, the silver ink can be considered as an example of a special color ink that can reproduce a metallic luster, for example.

  Further, in the printing apparatus 12, as the special color ink, ink of a color other than silver may be used. In general, special color inks include glossy inks such as metallic luster, inks of primary colors such as white and other CMYK inks, and special components such as fluorescent components. It is conceivable to use ink or the like containing.

  In addition, in the printing apparatus 12, in addition to the inks of the respective colors CMYK as the primary colors, it may be possible to further use a subset of primary colors having optical characteristics based on these primary colors. In this case, the spot color ink can be considered as an ink other than the primary color ink and its subset ink, for example. Further, in this case, the subset ink can be considered as, for example, ink for in charge of reproduction of a color gamut in a range that is difficult to reproduce with primary color inks such as CMYK colors. By using such a subset of ink, a wider color gamut can be reproduced. However, the subset ink is an ink of a subset of primary color inks, and is basically an ink of a color that conforms to a primary color such as each color of CMYK. In addition, the subset ink is also an ink that conforms to the subtractive color mixing method in the same manner as the primary color, and is assumed to be used in combination with the primary color ink. For this reason, it is usually difficult to reproduce a texture having an attractive property such as white or metallic luster even when a subset of ink is used. Of the textures that can be expressed by special color inks, metallic luster has particularly complex reflection characteristics because it exhibits different reflection characteristics depending on the incident angle of light. The silver ink is used, for example, to reproduce such a metallic luster texture.

  The color proofing PC 14 is a computer for color proofing, and displays the result of predicting the print result on the display device 16 and executes color proofing by accepting a user operation. In this case, the color calibration is an operation for adjusting a color printed by the printing apparatus 12, for example. Further, in this example, the printing apparatus 12 predicts the printing result for the printing result of the portion to be printed using each color of CMYK as the process color in the same or similar manner as the processing in the known color calibration. . Further, with respect to the print result of the portion to be printed using the silver color ink which is the special color ink, the print result is predicted using a model formula created in advance by a method described in detail later. Accordingly, in this example, color calibration is performed in consideration of the special color ink. Further, the color proofing PC 14 performs the above-described operation by using a model formula according to a program installed in advance, for example.

  The display device 16 is a display device (monitor device) of the color proofing PC 14 and displays an image indicating a printing result predicted by the color proofing PC 14 when the color proofing is executed. According to this example, for example, color calibration using a model formula can be appropriately executed. As the color proofing PC 14, it is also possible to use a configuration including a display device such as a notebook PC. In this case, it can be considered that the display device 16 in the printing device 12 is configured as a part of the PC 14 for color calibration.

  Next, a method for creating a model formula used in this example will be described in more detail. As described above, in this example, the model formula is used in the calculation performed to predict the print result in the color proofing PC 14. In this case, the model formula can also be considered as a formula used in an operation performed to display the predicted print result on the display device 16, for example. Further, as described above, in this example, BRDF is measured when the model formula is created. In this case, when creating the model formula, first, the printing device 12 is used to print (output) a printed material (printed output material) to be measured (measurement sample). As the measurement sample, for example, a patch (color patch) in which preset conditions are set is printed. In this case, the printed matter on which the patch is printed is an example of a printed matter for evaluation. The evaluation printed material is, for example, a printed material used for evaluating a printing result performed using ink.

  Further, in this example, when creating the model formula, a printed matter on which a plurality of patches with different print densities of the special color inks are printed is printed, and the BRDF is measured for each patch. In this case, the print density is the amount of ink per unit area. The amount of ink per unit area is, for example, the amount of ink ejected per unit area when each patch is printed. The print density can also be considered as, for example, the color density set in the input image for printing. In addition, the printed matter on which such a plurality of patches are printed can be considered as an evaluation printed matter including a pattern in which the print density is varied in a plurality of stages, for example. More specifically, in this example, for example, an ink jet printer capable of using silver ink is used, and the print density of the silver ink is sequentially changed at a predetermined step width (interval). Print multiple patches. In an experiment conducted by the inventors of the present application, a CJV150-107 type ink jet printer manufactured by Mimaki Engineering Co., Ltd. was used as the ink jet printer.

  Further, the plurality of patches is not limited to a patch using only silver ink, and for example, a patch combining silver and primary colors may be further printed. A patch combining a silver color and a primary color is, for example, a patch corresponding to a so-called color metallic color. In this case, it is also conceivable to print a plurality of patches by sequentially changing the print density with a preset width for the primary color ink (any color of CMYK) combined with the silver color. In this case, it is conceivable that the step size of the print density for the silver color ink and the primary color ink is, for example, about 10% (for example, about 5-15%). If comprised in this way, the printing which changed the printing density in steps, for example can be performed appropriately. When more detailed measurement is performed, it is preferable to set the print density step size to about 2%. Further, the print density step size is not set uniformly, but may be varied depending on the print density region. In this case, for example, a portion with a steep change in optical characteristics is preferable, and it is preferable to measure in detail. It is conceivable that all the step widths are about 10%.

  In addition, when the inventors of the present application have confirmed through various experiments and the like, it is considered that there is no problem with a printing density step size of about 20% in practice. Therefore, in order to reduce the man-hour required for BRDF measurement, the step size of the print density of the silver ink may be set to about 20% (for example, about 15 to 25%). Further, when printing a patch in which a silver color and a primary color are combined, it can be considered that the number of man-hours required for BRDF measurement increases as the number of patches increases. Therefore, in this case, it is conceivable that at least the step size of the printing density of the primary color ink is set to about 20%.

  The BRDF measurement for each patch is performed using, for example, a known variable angle spectrophotometer. As a known variable angle branching photometer, for example, a GCMS-4 apparatus which is a three-dimensional variable angle spectrocolorimetric system manufactured by MCRL can be suitably used. In the BRDF measurement performed in this example, regarding the measurement angle, initially, the incident angle was measured in the range of 0 ° to 80 ° at 1 ° intervals. In addition, with respect to the reflection angle, a range from −80 ° to 80 ° was measured at intervals of 1 °. After that, based on the initial BRDF measurement result, the interval was changed to 5 ° with respect to the incident angle of the portion with a low rate of change. Therefore, in the BRDF measurement performed when creating the model formula, for example, the incident angle and the reflection angle are partially measured at intervals of about 1 ° (for example, about 0.5 to 1.5 °), and other It is conceivable to measure the portions at intervals of about 5 ° (for example, about 3 to 8 °). FIG. 2A shows a part of the BRDF measurement result performed as described above as an example of the BRDF measurement result measured when the model formula is created. FIG. 2B shows an example of the output of the model formula regarding the prediction result performed using the model formula. In this case, the output of the model formula is a value calculated by the model formula. At the time of printing result prediction, for example, the printing result is predicted by using the output of a model formula as shown in FIG.

  FIG. 3 is a diagram for explaining in more detail how to create the model formula. FIG. 3A shows an example of a patch to be printed in this example. As described above, in this example, when a model formula is created, a plurality of patches with different print densities are printed, and BRDF measurement is performed for each patch. More specifically, in the case shown in FIG. 3 (a), Y and silver inks are used, and the density of each color ink is varied in a plurality of stages to perform patch printing. In the drawing, a plurality of quadrangles arranged vertically 4 and 11 horizontally indicate patches corresponding to each density. Also, the numerical value shown beside the character Sv in each square indicates the print density of the silver ink. The numerical value shown next to the letter Y indicates the print density of Y-color ink. In this case, as can be seen from the print densities of the respective colors shown in the figure, the step size of the print density of the silver ink is set to 10%. Further, the step size of the printing density of the Y color ink is set to 20%.

  The patch shown in FIG. 3A is an example of a patch in which silver and primary color inks are combined. Further, in this figure, for convenience of illustration and explanation, only the Y color among the primary colors is combined with the silver color. However, when printing an actual patch, primary colors other than Y (for example, at least one of M, C, and K) may be combined with the silver color as necessary. In this case, it is conceivable to print a patch in which the silver color and various primary colors are combined in the same or similar manner to the Y color in FIG. It is also conceivable to use inks of colors other than silver as the special color ink. In this case, it is preferable to print a plurality of patches with the printing density of the special color ink being the same as or different from the silver color ink in FIG.

  FIG. 3B is a flowchart illustrating an example of an operation for creating a model formula. In this example, when creating a model formula, as described above, a printed matter on which a plurality of patches are printed is printed (S102). In this case, a printed matter on which a plurality of patches are printed can be considered as an example of an evaluation printed matter including a pattern in which the print density is varied in a plurality of stages. The operation in step S102 is an example of a pattern printed material creation stage for creating an evaluation printed material including such a pattern. In this example, in step S102, a plurality of patches using silver and Y color inks are printed by printing the patches shown in FIG.

  After printing the patch, BRDF (bidirectional reflectance distribution function) is measured for each printed patch (S104). In this case, the operation in step S104 is an example of an operation in a measurement stage for measuring the BRDF for the evaluation printed material. Further, in this example, in step S104, BRDF is measured in association with the print density of each color ink used at the time of patch printing by measuring BRDF for each patch shown in FIG. . Further, in this case, the operation in step S104 can be considered as an operation for obtaining a spatial reflection characteristic for a printed matter printed using silver ink or the like, for example.

  Further, after the BRDF measurement, the model formula is calculated based on the measurement result (S106). In this case, the operation in step S106 is an example of the operation in the mathematical formula creation stage. In this example, in step S106, a model formula is calculated based on at least the BRDF associated with the print density by using the BRDF measurement result corresponding to each patch.

  More specifically, in this example, in step S106, the model formula is obtained by performing approximation (for example, Wiener estimation) using the least square method on BRDFs associated with a plurality of print densities. create. In this case, approximation such as Wiener estimation is performed for each combination of each incident angle and each reflection angle in BRDF. Further, the created model expression can be considered as, for example, a mathematical expression for estimating the correlation between the print density and BRDF. Also, the model formula can be considered as a formula for estimating the reflectance when printing is performed using a spot color, for example.

  In step S106, the model expression may be created using not only the BRDF measurement results for all patches, but only the BRDF measurement results for some patches. Also, as for the BRDF measurement results for each patch, the measurement results (spectral reflection data) for all angles (combination of incident angles and reflection angles) are not used, but only the measurement results for some angles are used. Also good. Also, in this case, by conducting preliminary experiments in advance, estimation is performed to clarify two parameters, the angle of spectral reflection data and the print density of patches, which are the minimum necessary for the creation of a model formula (modeling). Based on these parameters, it is conceivable to determine a patch, an angle, and the like used when creating the model formula. According to this configuration, for example, the model formula can be created more efficiently and appropriately by creating the model formula using the minimum necessary printing density.

  In this example, as the model formula, for example, a formula used for expressing the texture in PBRT, which is a physics-based ray tracing program, is calculated. With this configuration, for example, in a color calibration system that displays a printing result in a three-dimensional virtual space, a texture (for example, a metallic glossy texture) in a printing result using a special color ink using a model formula is used. Etc.) (simulation of texture) can be appropriately performed. Thereby, for example, in a color proofing system etc., prediction of a printing result can be performed appropriately.

  In addition, the inventor of the present application performs subjective evaluation of the texture reproduced by the model formula created as described above, in comparison with the printed matter (inkjet output matter, hard print) actually printed by the printing apparatus (inkjet printer). It was. In this case, the subjective evaluation is, for example, an evaluation performed based on a plurality of human subjects. In this case, the subjective evaluation can be considered as an evaluation performed on a simulation result (simulation model) using a model formula, for example. Further, this evaluation can be considered as an evaluation for comparing the reflection characteristics between the actually printed matter and the printed result (silver print) with the silver ink reproduced by the simulation. In this example, visual evaluation by a plurality of people is performed as subjective evaluation. Moreover, in this example, when performing the subjective evaluation described above and below, for example, it is conceivable to perform evaluation for obtaining the 95th percentile value. The inventor of the present application has confirmed from this subjective evaluation that a texture such as metallic luster can be appropriately reproduced by the model formula created as described above.

  As described above, the model formula can be appropriately created by measuring the BRDF with respect to the number of patches shown in FIG. 3A, for example. And in this case, considering the result of the above subjective evaluation and the like, for example, if a model formula with sufficient accuracy for the ability of the human eye is created, the formula is appropriately calculated without enormous man-hours. Can be considered to be able to create. More specifically, in this case, for example, it can be said that the number of patches necessary for creating a model formula corresponding to one color can be at least 11 or less. In this case, the model formula corresponding to one color is, for example, the print density and BRDF of a special color ink (for example, silver color ink) when other conditions (for example, the print density of primary color ink to be combined) are the same. It is a mathematical formula that estimates the correlation with. In addition, as described above, when calculating the actual model formula, it is not always necessary to use a patch corresponding to all the densities. Can be created. Therefore, the number of patches necessary for creating a model expression corresponding to one color can be set to 5 or less, or 3 or less, for example.

  As described above, according to the present example, for example, BRDF is measured for the optical characteristics of the special color ink, and the spatial reflection characteristic is acquired, so that it is used for reproducing the metallic luster or the like expressed using the special color ink. Model formulas can be created appropriately. Accordingly, for example, in a color calibration system for an ink jet printer or the like, it is possible to appropriately predict a printing result. In this case, the series of methods described above can be considered as a method for establishing a measurement method necessary for reproducing the texture of ink having a metallic luster, for example. In addition, this method can be considered as a method for constructing a simulation of a printed matter when a special color ink is used, for example. As for the operation of the flowchart shown in FIG. 3B, for example, an operation of measuring BRDF as the optical characteristic of the special color ink and modeling the reflection characteristic based on the measurement result can be considered.

  Next, a modified example of how to create a model formula will be described. In the above, the operation | movement etc. which produce a model formula mainly based on the measurement result of BRDF were demonstrated using FIGS. In addition, the fact that subjective evaluation was performed on the texture such as metallic luster reproduced using the model formula was explained. In this case, this subjective evaluation is performed after the model formula is created. On the other hand, the inventor of the present application has found that a model formula can be created more easily and appropriately by performing subjective evaluation in the operation of creating a model formula.

  4 and 5 are diagrams for describing a modification example of the operation of creating the model formula. FIG. 4 is a flowchart showing an example of an operation for creating a model formula in this modification. FIG. 5 is a diagram for explaining how to use the patch in this modification. Except as described below, the operation for creating a model formula in this modification is the same as or similar to the operation described with reference to FIGS.

  Also in the operation of this modified example, first, a printed material on which a patch, which is an example of a printed material for evaluation, is printed is the same as or similar to the operation in step S102 described with reference to FIG. S102). In this case, for example, as shown in FIG. 5A, the same patch as that shown in FIG. 3A is printed. Also in this case, BRDF measurement is performed in the same or similar manner to the operation in step S104 described with reference to FIG. However, in this modification, subjective evaluation is performed on the glossiness of each patch in parallel with the operation of step S104 (S103). In this case, the operation in step S103 is an example of an operation in the subjective evaluation stage. The subjective evaluation stage is a stage in which subjective evaluation is performed on the patch created in step S102, for example.

  More specifically, in this example, in step S103, for example, at least a part of a plurality of stages of print density is evaluated by subjective evaluation. In this case, selecting a part of a plurality of stages of printing density means, for example, selecting a part of patches from patches corresponding to various printing densities as shown in FIG. . In step S103, for example, it is conceivable to perform subjective evaluation by a known method such as the SD method (Semantic Differential Method). As a specific method of subjective evaluation, other known methods may be used. In this example, the subjective evaluation is performed by paying attention to the gloss expressed by the silver ink used as the special color ink. In addition, as such subjective evaluation, for example, by selecting a patch that allows a plurality of people to feel glossiness and performing an evaluation for obtaining the 95th percentile value, at least in association with the print density, is the glossiness felt? Evaluate whether or not.

  FIG. 5B is a diagram illustrating an example of a patch selected by subjective evaluation, and an example of a patch selected by subjective evaluation by painting a patch determined to be non-glossy by subjective evaluation black. Is shown. As can be seen from the figure, by performing such subjective evaluation, it is possible to appropriately select a patch corresponding to the print density indicating glossiness. In this case, as an operation for selecting a part of patches in step S103, for example, an operation for selecting a part of print density can be considered. In this case, it can also be considered that the patch determined to be glossy in the subjective evaluation indicates a range of metallic luster to be reproduced by the model formula. Therefore, the operation in step S103 can be considered as, for example, an operation for narrowing a range of metallic luster to be reproduced based on the result of subjective evaluation.

  Further, following the operations in steps S103 and S104, a model formula is calculated (S106). In step S106 of this modification, the BRDF measurement results for all patches shown in FIG. 5A are not used, but are associated with the patches (print density) selected in the subjective evaluation in step S103. A model formula is created based at least on the measured BRDF measurement result. In this case, for example, the approximation using the least square method is performed on the BRDF measurement results associated with some of the patches selected in step S103, so that FIG. The model formula is calculated in the same or similar manner to the operation in step S106 when described with reference to FIG. In this case, as a model formula corresponding to one color, for example, one model formula is created for a print density range including all print densities corresponding to the patch selected in step S103 for that color. Is preferred. If comprised in this way, a model formula can be produced appropriately based on the measurement result of BRDF, and the result of subjective evaluation, for example.

  Further, in this case, during the operation of creating the model formula, evaluation reflecting the human eye ability can be appropriately performed by subjective evaluation. In addition, by selecting some patches in the subjective evaluation and using the BRDF measurement results corresponding to the selected patches, a model formula can be obtained for the density range where glossiness is felt when viewed with human eyes. It can be created more appropriately. This also makes it possible to more appropriately create, for example, a model expression with sufficient accuracy for human eye ability. As described above, according to the present modification, for example, when a glossy special color ink such as a silver ink is used, the subjective evaluation can be appropriately performed. This also makes it possible to appropriately create a model formula using subjective evaluation, for example. In addition, when creating a model formula for the density range where glossiness is felt when viewed with the human eye, as in this modification, for example, create a model formula including the range where glossiness is not felt. This makes it possible to create a model expression with higher accuracy than in the case of doing so. In this case, it is also possible to reduce the number of patches to be measured by BRDF. Therefore, according to this modification, for example, it is possible to more appropriately create a high-precision model expression.

  Further, as described above, in the subjective evaluation performed in this modification, for example, as shown in FIG. 5B, a patch corresponding to the print density at which gloss is felt is selected. However, in this case, it is not always necessary to select patches corresponding to all print densities at which glossiness is felt, but patches corresponding to only a part of the print density at which glossiness is felt may be selected. . More specifically, when creating the model equation as described above, the print density at the end of the range where gloss is felt is particularly important. Therefore, in the subjective evaluation, after confirming the density range in which gloss is felt, a part of patches including a patch located at the end of the range may be selected instead of all the patches in the range. In this case, for example, it is conceivable to select a part of patches whose print density is shown in FIG. FIG. 5C is a diagram illustrating a modification example of the patch selected in the subjective evaluation, and an example of a selection method when selecting a patch corresponding to only a part of the print density at which glossiness is felt. Show. In this case, as shown in the drawing, only a part of the patches shown in FIG. 5B is selected as a patch used to create a model formula corresponding to one color.

  Here, the patch located at the end of this range can be considered as a patch corresponding to the end of the range where metallic luster is felt, for example. For at least one end patch, a patch corresponding to a point where the metallic luster is lost due to a change in print density can be considered. Further, regarding the method of selecting patches shown in FIG. 5C, more specifically, for example, when there are three or more patches that feel glossy among patches corresponding to one color, gloss is felt. It can be considered as a method of selecting a partial patch including at least two at both ends of the density range. In addition, when there are two or less patches that feel gloss for one color, it is preferable to select all patches that feel gloss. In addition, when there are four or more patches where gloss is felt for one color, it is preferable to select two patches at both ends of the density range where gloss is felt and one patch between them. Further, in this case, as one patch in between, for example, it is conceivable to select a patch at the center or near the center of the density range where gloss is felt. The patch near the center is, for example, the patch closest to the center. If comprised in this way, a model type | formula can be appropriately produced based on the measurement result of fewer BRDF with respect to the density range in which glossiness is felt, for example. In addition, when there are more patches that feel gloss for one color, it is also possible to select four or more patches including two at both ends of the density range where gloss is felt.

  Further, as is clear from the above description and the like, it is not always necessary to use the BRDF measurement results for all patches in order to create the model formula. However, in this modification, the subjective evaluation performed in step S103 and the BRDF measurement performed in step S104 are performed in parallel. In step S104, BRDF is measured for all patches, as in the case described with reference to FIG. This also measures the BRDF corresponding to all the print densities used during patch printing. When configured in this way, for example, BRDF measurement can be started at an early stage without waiting for the result of subjective evaluation. In addition, by measuring BRDF corresponding to more print densities regardless of the result of subjective evaluation, more available parameters can be ensured, for example, when various analyzes are performed thereafter. Also, such an effect can be obtained in the same way when, for example, subjective evaluation is performed after BRDF measurement. Therefore, for example, the operation in step S103 may be performed after the operation in step S104.

  Further, in a further modification of the operation of creating the model formula, for example, in order to perform BRDF measurement more efficiently, BRDF measurement may be performed after subjective evaluation is performed in the same or similar manner to step S103. . In this case, it is conceivable to measure only the BRDF corresponding to a part of the print density using the result of the subjective evaluation.

  FIG. 6 is a diagram for explaining a further modification of the operation for creating the model formula, and shows an example of the operation in the case where BRDF measurement is performed after the subjective evaluation is performed. Except as described below, the operation for creating a model formula in this modification is the same as or similar to the operation described with reference to FIGS.

  In this modification, when a model formula is created, for example, patch printing (S102) and subjective evaluation (S103) are performed in the same or similar manner to steps S102 and S103 described with reference to FIG. In this case, the BRDF measurement (S104) is performed using the result of the subjective evaluation after the subjective evaluation.

  More specifically, in the present modification, the man-hours required for BRDF measurement are greatly reduced by performing BRDF measurement only on patches selected by glossiness evaluation in subjective evaluation. In this case, for the BRDF measurement performed in the present modification, for example, only a part of the print density including at least the print density selected in the subjective evaluation among the print densities in a plurality of stages expressed by the plurality of patches. It can be considered as an operation for measuring the corresponding BRDF. In this case, in the subjective evaluation, for example, it is conceivable to select only the patch whose density is shown in FIG. If comprised in this way, the man-hour of the measurement of BRDF can be reduced appropriately, for example. In addition, for example, a model formula can be created more efficiently. In this case, by using subjective evaluation, a model formula can be created more appropriately even when only BRDF corresponding to a small number of types of print densities is measured, for example. Therefore, according to this modification, for example, prediction of a print result can be performed more easily and appropriately. Further, in this modified example, in the subjective evaluation, for example, more patches may be selected than the patch whose density is shown in FIG. In this case, for example, all patches that are judged to be glossy, such as patches whose density is shown in FIG. 5B, may be selected. Also when comprised in this way, the man-hour of the measurement of BRDF can be reduced appropriately, for example.

  Subsequently, supplementary explanations regarding each configuration described above, explanations of further modifications, and the like will be given. First, the effect of using the model formula described above will be described in more detail. In the following, for convenience of explanation, the components described above are collectively referred to as this example.

  As described above, according to the present example, for example, when a glossy special color ink such as a silver ink is used, the printing result is appropriately predicted using the model formula. Can do. In this case, it is conceivable to estimate the reflectance or the like in the model formula. If comprised in this way, prediction of a printing result can be performed appropriately, for example in a color calibration system etc. In this case, as a model formula corresponding to one color, for example, one common formula can be used for all print density ranges in which the reflectance is estimated. In this case, it is possible to directly and appropriately predict a printing result at a printing density other than the printing density actually expressed by the patch when the model formula is created.

  In addition, as described above, in this example, the print result is not predicted as precisely as possible, but the accuracy of the human eye is sufficiently accurate in consideration of the human eye ability. A model formula is being created. In this case, for example, in the BRDF measurement performed at the time of creating the model formula, the required man-hours can be greatly reduced as compared with the case where the print result is predicted as precisely as possible. Therefore, according to this example, it is possible to more easily and appropriately predict the printing result. Also, in this case, a model with sufficient accuracy for human eye performance by performing subjective evaluation in the operation of creating a model expression, such as the operation described with reference to FIGS. It is possible to create expressions more appropriately.

  Here, when considering the ability of human eyes, if adjustments are made by an operator (operator) who has some experience, it is appropriate to perform subjective evaluation that requires evaluation by multiple humans. It seems that color proofing can be done. However, in this case, there may be variations in the results of color calibration due to individual differences in the operator's sense. On the other hand, when performing the subjective evaluation as described above, it is possible to create a model formula that is more objectively matched to the ability of the human eye. Therefore, according to this example, for example, color calibration can be performed more appropriately.

  Further, regarding the subjective evaluation, in the above, the case where evaluation is made as to whether or not glossiness is felt in association with the print density has been described with reference to FIGS. However, the subjective evaluation is not limited to the presence or absence of glossiness, and other items may be further evaluated. In this case, for example, in the subjective evaluation performed in step S103 shown in FIG. 4 and FIG. 6, it may be possible to further evaluate the degree of gloss in association with the print density. If comprised in this way, when using the ink of a glossy special color, a more detailed subjective evaluation can be performed appropriately. Further, when the evaluation of the degree of gloss is further performed, in the subjective evaluation, for example, it is conceivable to evaluate the glossiness in a plurality of stages (for example, about 7 stages) by a known subjective evaluation method. In this case, it is preferable to create a model formula reflecting the evaluation result of the degree of gloss.

  Further, from the viewpoint of glossiness perceived by human eyes, even if the printing density is the same, it may be possible that a different impression is produced depending on the printed pattern. For this reason, when printing results are to be predicted in more detail, it is conceivable that printing results are predicted in consideration of the pattern to be printed. In this case, for example, as a plurality of patches to be printed at the time of creating the model formula, it is conceivable to print patches of a plurality of types of patterns. In this case, for example, it is conceivable to create a model formula for each pattern by printing a plurality of patches with different print densities for each pattern. If constituted in this way, prediction of a printing result can be performed with higher accuracy, for example.

  In this case, as the patch pattern, for example, a micro pattern determined according to the arrangement of ink dots, a macro pattern corresponding to a pattern expressed by printing, or the like may be used. In this case, as the micro pattern, for example, a pattern determined by a position (ink droplet landing position) at which ink is ejected from each nozzle of the inkjet head can be considered. Further, the micro pattern can be considered as, for example, a mask pattern used in a halftone process performed during printing, a pattern determined according to a spatial frequency, and the like. Further, a macro pattern can be considered as a pattern determined by the shape of a region to be filled with a constant printing density, for example. More specifically, for example, a pattern such as a solid pattern, a checkered pattern, or a striped pattern can be used as the macro pattern.

  In addition, the texture (such as metallic luster) expressed when printing using special colors may change depending on various printing conditions (for example, the number of passes, resolution, etc.) in addition to the print density and pattern. Conceivable. Therefore, it is preferable to create the model formula for each printing condition, for example. In addition, when a plurality of types of printing conditions can be used, for example, it is preferable to create a model formula corresponding to each printing condition by printing a plurality of patches for each printing condition.

  Moreover, in the above, the application of the model formula has been described mainly with respect to an example in the case of using it in a color calibration system. In this case, the model formula can be considered as, for example, a formula for obtaining parameters used for displaying an image on the display device 16 (see FIG. 1). However, the model formula created as described above may be used in a configuration other than the color calibration system. In this case, the model formula can be considered as a formula for predicting a printing result when printing is performed under a predetermined printing condition. In this case, the model formula is not necessarily used for display on the display device 16 but may be used in various systems for predicting the printing result.

  In recent years, inkjet technology has been studied for application in various industrial fields because it can be printed at low cost and with high definition. In addition, as such an applied technology, for example, formation of a metal wiring by using a special color ink containing a conductive metal material or the like and printing on an electronic substrate or the like by an ink jet method has been studied. . In this case, for example, it is conceivable to predict the state of the formed wiring by using the above model formula in the system for predicting the state of the formed wiring.

  The present invention can be suitably used, for example, in a method for creating a printing result prediction formula.

DESCRIPTION OF SYMBOLS 10 ... Printing system, 12 ... Printing apparatus, 14 ... Color calibration PC, 16 ... Display device

Claims (12)

A method for creating a print result prediction formula that creates a print result prediction formula that is a formula used to predict a print result using ink,
The evaluation printed matter including a pattern in which a printed matter for evaluation, which is a printed matter used for evaluation of a printing result performed using the ink, is prepared, and a print density which is an amount of ink per unit area is varied in a plurality of steps. A pattern printed matter creation stage to create,
Measuring a bidirectional reflectance distribution function for the printed matter for evaluation, and measuring a bidirectional reflectance distribution function in association with the print density;
The printing result prediction formula is calculated based on the measurement result in the measurement step, and the printing result prediction formula is created based at least on a bidirectional reflectance distribution function associated with the print density. A method for creating a mathematical expression for predicting a print result, comprising: a mathematical expression creating stage. It is a step of performing a subjective evaluation on the printed matter for evaluation created in the pattern printed matter creation step, further comprising a subjective evaluation step of selecting at least a part of the print density of the plurality of steps by subjective evaluation,
In the mathematical expression creating step, a printing result prediction mathematical expression is created based at least on a bidirectional reflectance distribution function associated with a part of the printing density selected in the subjective evaluation stage. How to create formulas for predicting results.   3. The method for creating a printing result prediction formula according to claim 2, wherein in the measuring step, a bidirectional reflectance distribution function corresponding to all of the printing densities in the plurality of steps is measured. The measurement step is a step performed after the subjective evaluation step,
Measuring the bidirectional reflectance distribution function corresponding to only a part of the print density including the print density selected in the subjective evaluation stage among the print densities of the plurality of stages in the measurement stage; The method for creating a mathematical expression for predicting a print result according to claim 2. As the ink, a glossy special color ink is used,
5. The print result prediction formula generation according to claim 2, wherein, in the subjective evaluation stage, evaluation is performed as to whether or not glossiness is felt at least in association with the print density. Method.   The method for creating a printing result prediction formula according to claim 5, wherein silver ink is used as the glossy special color ink.   7. The method for creating a printing result prediction formula according to claim 5 or 6, wherein in the subjective evaluation stage, the degree of gloss is further evaluated in association with the printing density.   In the mathematical formula creation step, the subjective evaluation is performed by approximating the bidirectional reflectance distribution function associated with a part of the print density selected in the subjective evaluation step using a least square method. 8. The print result prediction formula according to claim 2, wherein one print result prediction formula is created for a print density range including all of the print densities selected in the step. How to create   9. The method for creating a printing result prediction formula according to claim 2, wherein printing using the ink is performed by an inkjet method.   10. The method for creating a print result prediction formula according to claim 1, wherein the print result prediction formula is a formula used in an operation performed to display the predicted print result on a monitor. . There is a prediction method for predicting the printing result when printing using ink,
Predicting the printing result using the printing result prediction formula created by the method for creating a printing result prediction formula according to any one of claims 1 to 10,
A prediction method comprising displaying an image indicating the predicted printing result on a display device. There is a prediction system for predicting the printing result when printing using ink,
Predicting the printing result using the printing result prediction formula created by the method for creating a printing result prediction formula according to any one of claims 1 to 10,
A prediction system, wherein an image showing the predicted printing result is displayed on a display device.